1. Field of the Invention
The present invention relates to an immersion exposure apparatus which is capable of measuring reflectance of an optical element constituting a projection optical system and a device manufacturing method using thereof.
2. Description of the Related Art
In a manufacturing process of semiconductor devices constituted by fine patterns such as a ULSI, a reduced projection exposure apparatus which performs a reduced projection of a pattern formed on an original plate onto a substrate on which a photosensitizing agent is applied so as to transfer it is used. In accordance with the improvement of the integration density in semiconductor devices, further miniaturization of the pattern is required, and an exposure apparatus has responded to the miniaturization as well as the development of resist processes.
In order to improve the resolution of the exposure apparatus, generally, there are a method for shortening an exposure wavelength and a method for enlarging numerical aperture (NA) of a projection optical system.
In order to enlarge the numerical aperture (NA), a projection exposure apparatus using an immersion method has been proposed in the past. Conventionally, the space between a final surface of a projection optical system and a substrate to be exposed (for example, a wafer) was filled with gas. In contrast, according to the immersion method, this space is filled with liquid in order to perform a projection exposure.
The advantage of the immersion method is to improve the resolution compared to the conventional method even if a light source that has the same wavelength as that of conventional one is used. For example, in a case where the liquid that is filled with the space between the projection optical system and the substrate is pure water (the refractive index is 1.44), when a maximum incident angle of a light beam that forms an image on a substrate is assumed to be equal between the immersion method and the conventional one, the resolution of the immersion method improves 1.44 times as much as the conventional one. This is equivalent to increasing the numerical aperture NA 1.44 times as much as the projection optical system of the conventional method. Thus, the immersion method enables to obtain the resolution more than NA=1, which was conventionally impossible.
Japanese Patent Laid-Open No. 2005-116570 discloses an immersion exposure apparatus in which a light receiving unit is placed on a substrate stage. This immersion exposure apparatus exposes a substrate by irradiating exposure light for the substrate (wafer) placed on a image surface of a projection optical system via the projection optical system and liquid.
The exposure apparatus disclosed in Japanese Patent Laid-Open No. 2005-116570 includes the light receiving unit which receives light that has passed through the projection optical system via a slit opening placed on an image surface of the projection optical system, and a temperature sensor which detects temperature information of the liquid filled between the projection optical system and the slit opening. Based on the result detected by the light receiving unit and the result measured by the temperature sensor, performance information including an imaging performance is calculated and this information is reflected at the time of exposure.
Japanese Patent Laid-Open No. 2005-191557 discloses that a plan plane having a water repellent flat surface at the substantially same height as that of the substrate (the wafer) on a substrate stage is provided and that the plan plane is configured to be exchangeable. Further, Japanese Patent Laid-Open No. 2005-191557 discloses that the surface of the reference member that is placed on the substrate stage and that has a reference mark also has water repellent properties and that the reference member is exchangeable. It also discloses that polytetrafluoroethylene is used as a material that has water repellent properties.
FIG. 9 is a plan view showing a configuration example of a wafer stage 5.
At a periphery outside the wafer 51, a wafer stage upper surface cover 47 and a light intensity sensor 4 are placed. In the immersion exposure apparatus, an immersion area 70 is larger than an exposure area (not shown). The wetted area 71 is larger than the immersion area 70. The wetted area 71 is an area which contacts liquid by the movement of the immersion area 70 in accordance with the exposure operation. A light intensity sensor 4 for controlling the exposure amount may be included in the wetted area 71.
The wafer 51, the water stage upper surface cover 47, and the light intensity sensor 4 are configured so that the heights of the surfaces which contact the liquid are the same one another. In this case, a water repellent process of the wetted surface is necessary. When the wafer stage 5 is driven in a state where the liquid remains, the residual liquid is splashed. It may causes the change of the environment inside the exposure apparatus (for example, rust is generated) or the generation of an electric fault.
A photoresist for immersion exposure (not shown) is applied on the wafer 51. This photoresist layer has water repellent properties. The water repellent process is performed on the wetted surface of the wafer stage upper surface cover 47 and the wetted surface of the light intensity sensor 4.
As described above, Japanese Patent Laid-Open No. 2005-191557 discloses that the reference member (a substrate reference plate) which has the reference mark to be irradiated by light has water repellent properties, the reference member is exchanged at the time of the deterioration of the water repellent properties, and polytetrafluoroethylene is used as a material having water repellent properties.
However, when an excimer laser light, particularly ArF excimer laser light, is irradiated on polytetrafluoroethylene, the water repellent properties are deteriorated and contaminants are generated. Therefore, the contaminants adhere to the wetted surface of the optical element which constitutes the projection optical system, and it may causes the generation of a defect at the time of exposing a wafer.